Revert "mm/pagewalk.c: walk_page_range should avoid VM_PFNMAP areas"

This reverts commit 2d140983b007b70dfe673af76fec5edbb9f511b1.

Change-Id: Id309386cd8d29efa8c62d95834d6d4dceed0c9a2
Merge remote-tracking branch 'CM/cm-11.0' into cm-11.0